Download Voltage in a circuit

Voltage and resistance in a
circuit
Level 1 Science
• Voltage is the amount of energy
carried by the charged electrons
(current) in the circuit.
• Thus, the voltmeter measures
the change in electron’s energy
between entering and leaving a
component so it has to be
connected in parallel to that
component.
• An electrons voltage
decreases as it goes through a
component.
• The unit of voltage is the volt
and the symbol is V
• Alessandro Volta
• Power packs and batteries
give electrons energy.
• This energy is all used up
getting through the circuit until
the electron gets back to the
power pack or battery where it
gets re-energised (or
recharged).
For example:
• an electron comes out of a
power pack with 12 volts of
energy.
• It might use 11 volts
getting through a light bulb
and 1 volt getting through
the wires.
• The electron gets back to
the power pack with no
energy.
• The electron then gets 12
more volts of energy which
it uses up as it goes around
the circuit again.
Energy Conversion
• An electron goes into a circuit
component with some energy
and comes out of it with less.
• Voltage measures how much
energy an electron loses as it
goes through a circuit
component.
• Circuit components are energy
converters - they might
convert electrical energy to :
light if the component is a
bulb,
heat (heaters),
sound (speakers),
movement (motors),
magnetism (solenoids).
Connecting voltmeters
• Voltmeters are also connected
across components red
terminal to red terminal in
parallel. (Touch test)
Energy of electrons
• When electrons leave their
power source, they have a
certain amount of energy. They
lose all their energy as they
pass through components and
they must return to the power
source with 0 Volts.
SERIES
• Voltages
across each
component
ADDS to total
voltage
• In a series circuit the lamps
are dimmer because they have
less power ( ½ I and ½ V).
PARALLEL
• The
voltage in
any loop in
a circuit
will = 0
With identical components parallel paths
will have the same voltage.
What goes in must come out.
12V given to
each
electron
12V removed from each electron
In a parallel circuit the lamps
are bright because they each
get the full energy of the
electrons passing through
them.
Resistance is a property of a
substance that limits the
flow of electrons through it.
Conductors have a very low
resistance.
Insulators have a very high
resistance.
• The bigger the resistance
the lower current.
Resistance enables a component
to convert electrical energy to
another form of energy.
ie - heating coils convert electrical
E to heat E
- lamp filaments convert electrical
E to heat E and then to light E.
- electrical motors convert elec E to
magnetic E to get kinetic E.
Resistance can be an advantage if
we wish to create heat (as in a
toaster)
or it can be a disadvantage if we
don’t want to create heat (as in an
electric motor).
Limiting heat loss in a circuit:
- a short length of wire has
less resistance than a long
length of wire.
- a good conductor has less
resistance than a poor
conductor.
-a low current creates less
resistance than a high current.
Resistance is calculated by:
R=
V
I
Where R = resistance
measured in ohms (),
V = voltage measured in
volts (V),
I = current measured in
amps (A).
Temperature and Resistance
When the temperature of a
conductor is kept constant, its’
resistance stays constant =
Ohms Law
As the temperature of a
conductor increases, so does
its resistance.
Power
Is a measure of how quickly
electrical energy is converted
into other forms of energy.
Power is measured in watts
(W).
1W is equal to 1 joule per
second.
Power Calculations
Power = Voltage X Current
P=VI
Where P is measured in
watts (W),
V is measured in volts, and
I is measured in amps
Electricity at Home
Mains power is 240V AC.
AC means the current changes
direction 50 times per second and
is said to be 50 Hertz (50 Hz).
Fuses are used to protect people
and property. They melt when the
current gets too high.
3 Pin Plugs
Neutral
Phase
Blue
Red
Earth
Yellow and Green
Current flows from phase to
neutral.
The Earth wire is a safety wire
to protect people from any
short circuit.